Practical signal‐to‐noise ratio quantification for sensitivity encoding: Application to coronary MR angiography

Purpose: To develop and evaluate a practical method for the quantification of signal‐to‐noise ratio (SNR) on coronary MR angiograms (MRA) acquired with parallel imaging. Materials and Methods: To quantify the spatially varying noise due to parallel imaging reconstruction, a new method has been implemented incorporating image data acquisition followed by a fast noise scan during which radiofrequency pulses, cardiac triggering and navigator gating are disabled. The performance of this method was evaluated in a phantom study where SNR measurements were compared with those of a reference standard (multiple repetitions). Subsequently, SNR of myocardium and posterior skeletal muscle was determined on in vivo human coronary MRA. Results: In a phantom, the SNR measured using the proposed method deviated less than 10.1% from the reference method for small geometry factors (≤2). In vivo, the noise scan for a 10 min coronary MRA acquisition was acquired in 30 s. Higher signal and lower SNR, due to spatially varying noise, were found in myocardium compared with posterior skeletal muscle. Conclusion: SNR quantification based on a fast noise scan is a validated and easy‐to‐use method when applied to three‐dimensional coronary MRA obtained with parallel imaging as long as the geometry factor remains low. J. Magn. Reson. Imaging 2011;33:1330–1340. © 2011 Wiley‐Liss, Inc.